A crossbar switch generally operates to connect any one of a first plurality of signal ports to any one of a second plurality of signal ports. Generally, signal ports in the first and second pluralities of signal ports are bi-directional and any of the first or second ports in the crossbar switch can be used to both receive and transmit signals. The crossbar switch operates as a router that routes a signal received on any one of its ports in the first or second plurality of ports to a desired port of the other of the first and second plurality of ports from which the signal is transmitted. Crossbar switches are typically used, for example, for routing signals in communication networks such as LANs, WANs, and telecommunication networks and in routing data signals between processors comprised in parallel data processing systems.
In many communication networks, signals are optical signals that are transmitted along optic fibers and routing is accomplished by optical crossbar switches. A first plurality of signal ports are ends of a first plurality of optic fibers and a second plurality of signal ports are ends of a second plurality of fibers. The crossbar switch operates to optically couple an end of a given fiber of the first plurality of optic fibers to an end of a given fiber of the second plurality of optic fibers, to provide a desired connection.
Optical crossbar switches are often required to accommodate very large numbers of optic fibers. As the number of fibers increases, the task of efficiently managing connecting and disconnecting large numbers of optic fiber ends without fibers becoming entangled becomes increasingly complex. Prior art crossbar switches for optically coupling and uncoupling large numbers of optic fibers tend to be complicated, unwieldy pieces of equipment that require relatively large volumes of operating space to accommodate the coupling and uncoupling operations.
U.S. Pat. No. 5,613,021, the disclosure of which is incorporated herein by reference, describes an optical crossbar switch in which a robot hand connects and disconnects ends of a plurality of first fibers to ends of a plurality of second fibers, which second fibers have their ends held stationary in a rectangular array in a coupling board. As an end of a fiber in the first plurality of fibers is connected or disconnected to an end of a fiber in the second plurality of fibers, length of the first fiber is respectively played out or “reeled in” by a fiber length adjusting unit which requires its own significant space volume. The robot hand “mimics” the way in which a human switch board operator operates a telephone switch board, plugging and unplugging telephone cables from a switch board. During operation of the switch, first optic fibers cross each other as they are connected and unconnected from different second optic fibers. In an embodiment of the invention, the adjusting unit comprises a pair of rotatable reels on which surplus portions of the first fiber are wound. The reels are spring loaded to urge them apart and take up slack in the fiber wound between them.
U.S. Pat. No. 6,307,983, the disclosure of which is incorporated herein by reference, describes an optical crossbar switch in which patch fibers are used to connect ends of a plurality of first fibers to ends of a plurality of second fibers. A first end of each of the patch fibers is connected to an end of a first fiber. The ends of the second fibers are mounted to a circular holding ring. The second ends of the patch fibers are mounted to a linear conveyor. The conveyor sequentially loads the second end of each patch fiber at a different desired loading location on the perimeter of a “loader ring”, which is coaxial with the holding ring that holds the ends of the second fibers and has a same diameter as the holding ring. The second end of a patch fiber is loaded to the desired location on the loader ring by suitably rotating the loader ring about the axis of rotation and translating the linear conveyor so that the position of the second end of the patch fiber on the linear conveyor meets the desired location on the loader ring perimeter. After the loading ring is loaded with the second ends of the patch fibers, the loading ring is translated along the common axis it shares with the holding ring to “dock” the second ends of the patch fibers with the ends of the second fibers. A configuration of connections between the first and second pluralities of fibers is determined by the positions of the patch fiber second ends on the loader ring and an azimuth angle of the loader ring relative to the holding ring.
PCT publication WO 02/43432, the disclosure of which is incorporated herein by reference, describes an optical crossbar switch in which any given one of a plurality of first optic fibers is optically coupled to any given one of a plurality of second optical fibers by translating the ends of the given fibers along different linear trajectories.